A number of patents and publications are cited herein in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Each of these references is incorporated herein by reference in its entirety into the present disclosure, to the same extent as if each individual reference was specifically and individually indicated to be incorporated by reference.
Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise,” and variations such as “comprises” and “comprising,” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.
It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a pharmaceutical carrier” includes mixtures of two or more such carriers, and the like.
Ranges are often expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment.
This disclosure includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Temozolomide
Temozolomide (also known as 3,4-dihydro-3-methyl-4-oxoimidazo[5,1-d]-1,2,3,5-tetrazine-8-carboxamide; 8-carbamoyl-3-methylimidazo[5,1-d]-1,2,3,5-tetrazin-4(3H)-one; methazolastone; M & B 39831; CCRG-81045; NSC-362856; Temodal; Temodar) is a well known anti-neoplastic agent that acts as an alkylating agent. Its primary application is in the treatment of brain cancer (e.g., glioma).

Temozolomide is a prodrug, being cleaved in a multi-step pathway firstly to liberate an unstable monomethyltriazene (MTIC), which then suffers proteolytic fragmentation to generate a highly-reactive methylating agent (methanediazonium ion) and 5-aminoimidazole-4-carboxamide (see, e.g., Arrowsmith et al., 2002, J. Med. Chem., Vol. 45, pp. 5458-5470). Support for this process comes from the isolation of MTIC from the degradation of temozolomide in aqueous sodium carbonate solution (see, e.g., Stevens et al., 1984, J. Med. Chem., Vol. 27, pp. 196-201). There is only a small pH window around physiological pH where ring-opening of temozolomide is accompanied by fragmentation of MTIC in a methylating mode.
The methanediazonium active species derived from MTIC (or temozolomide) is believed to covalently methylate guanine residues of DNA in tracts of three or more guanines (see, e.g., Hartley et al., 1988, Carcinogenesis, Vol. 9, pp. 669-674; Clark et al., 1995, J. Med. Chem., Vol. 38, pp. 1493-1504). The significant site of DNA methylation is the O-6 position of guanine residues and tumours which express high levels of the DNA repair protein O(6)-methylguanine methyltransferase (MGMT; also known as ATase) are inherently resistant to the drug (see, e.g., Wedge et al., 1996, Br. J. Cancer, Vol. 74, pp. 1030-1036; Lee et al., 1994, Br. J. Cancer, Vol. 69, pp. 452-456.) These studies have been reviewed (see, e.g., Stevens and Newlands, 1993, Eur. J. Cancer, Vol. 29A, pp. 1045-1047; Newlands et al., 1997, Cancer Treat. Rev., Vol. 23, pp. 35-61). O-6 guanine methylation is a cytotoxic (antitumor) lesion since it provokes base mis-pairing with thymine during DNA replication. Unless repaired by MGMT, mis-pairing on the daughter strand is recognised by mismatch repair proteins which trigger futile cycles of thymine excision and re-insertion leading to persistent DNA strand breaks.
In a significant development in our understanding of the molecular determinants influencing tumor responses to temozolomide, it is now clear that the promoter methylation status (at cytosine C-5 in CpG sequences of the MGMT gene) is a powerful predictor of clinical outcome in glioblastoma patients (see, e.g., Hegi et al., 2004, Clin. Cancer Res. Vol. 10, pp. 1871-1874; Hegi et al., 2005, New England J. Med., Vol. 352, pp. 997-1003). Tumors with the MGMT gene switched off, as in some brain tumors, are unable to repair the O-6 guanine lesions and are particularly sensitive to temozolomide. Conversely, most common tumors with the MGMT repair gene switched on, leading to high cellular levels of MGMT, can repair the O-6 guanine lesions and are resistant to the drug. This epigenetic feature considerably restricts the spectrum of action of temozolomide and its penetration of the cancer market.
A new strategy to overcome these deficiencies proposes that compounds structurally related in structure to temozolomide and retaining the drug's favourable pharmaceutical profile—such as ease of synthesis, acid stability, oral bioavailability, freedom from metabolic complications, transmission across the blood-brain barrier, and an acceptable toxicological profile—could be developed which create an alternative anti-tumor lesion at O-6 residues of guanines in DNA (i.e., not methylation) which cannot be repaired by MGMT. Such compounds would be likely to retain useful therapeutic activity against all brain tumors, but also those major killer tumor types (e.g., lung, breast, ovarian, colorectal, renal, pancreatic, melanoma) which are currently inherently resistant to temozolomide.
Temozolomide is the subject of granted claim 13 of U.S. Pat. No. 5,260,291 to Lunt et al. granted 9 Nov. 1993.
Certain 3-substituted-4-oxo-3,4-dihydro-imidazo[5,1-d][1,2,3,5]tetrazine-8-carboxylic acid amide (3™) compounds are described in international patent application number PCT/GB2008/004140 filed 16 Dec. 2008 (published as WO 2009/077741 on 25 Jun. 2009).